In the operation of spark-induced or spark-ignition combustion engines, and particularly automotive engines operating on gasoline, the octane number of the fuel must be high enough to prevent knocking. Gasolines sold at service stations typically have an octane number of from 87 to 93. Fuels having such octane numbers are satisfactory for most automotive engines.
For high performance engines, and for racing engines in particular, fuels of even higher octane numbers are required. The lower the octane number, the more likely it is that knocking will occur. The production of fuels of progressively higher octane values is progressively more difficult to achieve. In particular, fuels having an octane value at or above 100 are highly desired and the most difficult to produce. This is particularly true for unleaded fuels.
Current racing fuels, and particularly racing fuels for endurance racing, require not just high octane but optimized engine and fuel efficiency.
Currently many countries also impose a requirement in gasolines of an amount of bio-component: a component that has been derived from biological sources such as cellulose or plant materials, rather than from crude oil. It is expected that both racing fuel technical specifications, and eventually legislation, will require increased amounts of bio-component.
Common bio-components include alkanols, such as methanol and ethanol, obtained from natural sources, such as plant products and often termed, for example, bio-methanol and bio-ethanol.
WO 2010/014501 proposes an unleaded fuel composition comprising:
45 volume % or more of one or more branched paraffins;
34 volume % or less of one or more mono- and di-alkylated benzenes;
from 5 to 6 volume % of one or more linear paraffins having from 3 to 5 carbon atoms; and,
one or more alkanol having from 2 to 4 carbon atoms in an amount sufficient to boost the octane number of the unleaded fuel composition to 93 or greater, the unleaded fuel composition being free of any other ingredient or combination of ingredients that increases the octane number of the unleaded fuel composition by more than 1.0 unit.
The primary source for the branched paraffin component exemplified is refinery alkylate. The alkanol (bio) component exemplified is ethanol and used in an amount of 10 vol. % of total composition, excluding any fuel additive.